You are correct! TIL, and thank you. Connection processes get a SIGQUIT, shared buffers cleared, and WAL replayed, but postmaster stays alive. It's effectively an online restart.
What's online about this restart? Just that the tcp port keeps listening? I assume all running transaction will have to be aborted, right? And connections dropped?
I’d be very curious to hear what an online restart approach for sketchy extensions crashing a shared thread per connection process might look like. This is more a question for the author of the project but I’m curious if they have plans in that direction.